Ceramic Susceptor

ABSTRACT

Ceramic susceptor whose wafer-retaining face has superior isothermal properties, and that is suited to utilization in apparatuses for manufacturing semiconductors and in liquid-crystal manufacturing apparatuses. In plate-shaped sintered ceramic body  1 , resistive heating element  2  is formed. Fluctuation in pullback length L between sintered ceramic body outer-peripheral edge 1 a  and resistive heating element substantive-domain outer-peripheral edge  2   a  is within ±0.8%, while isothermal rating of the entire surface of the wafer-retaining face is ±1.0% or less. Preferable is a superior isothermal rating of ±0.5% or less that can be achieved by bringing the fluctuation in pullback length L to within ±0.5%.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to heaters in ceramics, and relates inparticular to heaters in ceramic susceptors employed in CVD devices,plasma CVD devices, etching devices, and plasma etching devices formanufacturing semiconductors, and in liquid-crystal manufacturingapparatuses.

2. Background Art

In order for the film-formation rates or etching rates in CVD (chemicalvapor deposition), plasma CVD, etching, or plasma etching on asemiconductor wafer retained in a film-deposition chamber to take placeuniformly, the wafer surface temperature must be strictly controlled.For the purpose of such temperature control, a heater is built into awafer-retaining member, the surface of the wafer-retaining member isheated, and a wafer of semiconductor material is heated by thermaltransfer. Ceramics endowed with heat-resistant, corrosion resistant andinsulative properties, such as aluminum nitride and silicon nitride,have been employed to date as wafer retaining members of this sort.

A wafer retaining member made of ceramic into which the foregoing heateris built then has been manufactured according to a method that amountsto sintering aluminum nitride and building-in a molybdenum coil, bytraining a molybdenum coil into a groove formed in for example adisk-shaped aluminum nitride plate, sandwiching it with another suchaluminum nitride plate, and hot-press sintering the sandwich.

In a wafer retaining member made of ceramic into which a heater isbuilt, i.e., a ceramic susceptor, the constituent components of theheater resistive heating element are regarded as elemental impurities,even in trace amounts, with respect to a semiconductor material forsilicon wafers or the like, or a liquid crystal material, and can becomethe source of malfunctioning in semiconductor chips and liquid crystals.

Given the impurity threat, either a resistive heating element must becompletely embedded into a ceramic susceptor so as not to appear on thesurface, or else a resistive heating element formed superficially on aceramic must be coated with a protective layer, within the chamber ofsemiconductor manufacturing apparatuses. Consequently, an area in whichthe heating element is not buried, i.e., a non-heating area, willnecessarily be present on the outer peripheral portion of the ceramicsusceptor. The heat generated by the resistive heating element istransmitted through the ceramic, reaching the surface, and from thesurface then radiates or escapes via gases due to heat transfer. Thismeans that in disk-shaped or rectangular plate-shaped ceramic susceptorsthe outer peripheral margin is therefore the place where heat is mostliable to escape.

Owing to the above-noted two causative factors taken together, the outerperiphery of a ceramic susceptor is the portion where temperature ismost prone to drop. To address this issue, elimination of difference intemperature by using for the ceramic a material whose thermalconductivity is high, to swiftly diffuse toward the outer periphery theheat generated by the resistive heating element, has been practiced.Likewise another expedient has been to try to eliminate the temperaturedifference by increasing the winding density of the coil and the patterndensity of the resistive heating element the more toward the outerperiphery of the resistive heating element they are, to raise theheating density along, compensating with heat in, the outer periphery.

When a coil trained into a groove in a molded ceramic body is sandwichedbetween molded ceramic bodies and worked in a hot press, however, itbecomes squashed into an indefinite shape and the outer peripheral edgeof the resistive heating element in its substantive domain becomesdisrupted. The consequence of this has been that despite a resistiveheating element being isothermally designed by strictly reckoning howmuch heat it puts forth and compensation for heat dispersion to itsnon-heated portions and for heat escape from its edge portion, inpractice, the substantive heat-issuing domain becomes disrupted in theedge portion, which has made it impossible to obtain desired isothermalrating in the surface entirety of the ceramic susceptor.

Meanwhile, with the scaling-up of semiconductor wafer size in recentyears, isothermal demands on ceramic susceptors for heating the wafershave become stricter, with an isothermal rating in the wafer-retainingface of at minimum within ±1.0%, preferably within ±0.5% being required.

SUMMARY OF INVENTION

An object of the present invention, in view of such circumstances todate, is to realize a ceramic susceptor, being a plate-shaped sinteredceramic body into which a coil-shaped resistive heating element isembedded, whose wafer-retaining face excels in isothermal propertiesover its entire surface.

In order to achieve the foregoing objective, a ceramic susceptor thatthe present invention realizes, being a resistive heating element formedin a plate-shaped sintered ceramic body, is characterized in thatfluctuation in pullback length between the outer peripheral edge of thesintered ceramic body and the outer peripheral edge of the resistiveheating element in its substantive domain is within ±0.8%. Furthermore,fluctuation in the pullback length is preferably within ±0.5%.

A ceramic susceptor by the present invention as noted above may becharacterized in that the sintered ceramic body is made of at least onesubstance type selected from aluminum nitride, silicon nitride, siliconcarbide, and aluminum oxide. Furthermore, the resistive heating elementmay be characterized in being made of at least one metal type selectedfrom W, Mo, Ag, Pt, Pd, Ni and Cr.

As determined by the present invention, in terms of a ceramic susceptorin which a coil-shaped resistive heating element is embedded into aplate-shaped sintered ceramic body, by controlling fluctuation in thepullback length between the outer peripheral edge of the sinteredceramic body and the outer peripheral edge of the resistive heatingelement in its substantive domain, the isothermal rating over thesurface entirety of the wafer-retaining face can be made the ±1.0% orless that has been demanded; more preferably, an isothermal rating thatis an outstanding ±0.5% or less can be achieved.

From the following detailed description in conjunction with theaccompanying drawings, the foregoing and other objects, features,aspects and advantages of the present invention will become readilyapparent to those skilled in the art.

BRIEF DESCRIPTION OF DRAWINGS

The FIGURE is a plan view illustrating an example of a circuit patternfor a resistive heating element.

DETAILED DESCRIPTION

The present inventors discovered as a result of concerted investigationsthat when forming a resistive heating element in a sintered ceramicbody, by getting the fluctuation in pullback length between the sinteredmember outer peripheral edge and the resistive heating elementsubstantive-domain outer peripheral edge to be essentially within ±0.8%,the isothermal rating of the ceramic susceptor over its entire facesatisfies the minimal requirement that it be within ±1.0%.

They likewise discovered that by getting the fluctuation in pullbacklength between the sintered ceramic body outer peripheral edge and theresistive heating element substantive-domain outer peripheral edge to beessentially within ±0.5%, the isothermal rating of the ceramic susceptorover its entire face will be the within ±0.5% that has been mostdesirable.

An example of a resistive heating element embedded in a sintered ceramicbody is illustrated in The FIGURE. The resistive heating element 2 thatis embedded in the sintered ceramic body 1 is formed into a coil-shapedcircuit pattern, and length L between outer-peripheral edge 1 a of thesintered ceramic body 1 and resistive heating element substantive-domainouter-peripheral edge 2 a of resistive heating element 2 is the pullbacklength. It will be appreciated that through lead lines from its twocircuit ends 2 b, 2 b the resistive heating element 2 forming the coilshape is rendered externally accessible, wherein supplying electricpower from a power source causes it to generate heat. Likewise it shouldbe understood that the circuit pattern shown in The figure for theresistive heating element 2 is a single example, and does not mean thatthe present invention is thereby limited.

In a situation in which the circuit pattern for the resistive heatingelement is formed onto a molded ceramic body or a green sheet, sinteringthe substrate and the circuit pattern proceeds while it is shrunk andmade compact. In such cases, shrinking uniformly is extremely difficultowing to non-uniform volatilization of oxides as the sintering promoter,which is due to non-uniformity in the sintering promoter and non-uniformcarbon residues after degreasing, and to fluctuations in the furnaceinternal temperature and atmosphere when sintering, and the conformationof the domain in which the resistive heating element is substantiallypresent is liable to warp. By the same token, hot press sintering amolybdenum coil shaped as a heater, and a molybdenum sheet, placed on amolded ceramic body deforms the outer peripheral edge of the resistiveheating element substantive domain because in the hot-press sinteringprocess the coil and the sheet become smashed and crushed or warped ordisplaced.

Although the outer peripheral edge of the sintered ceramic body can beprocessed to lend it precision, if the resistive heating elementsubstantive domain deforms, fluctuations will end up occurring in thepullback length between the sintered ceramic body outer peripheral edgeand the resistive heating element substantive-domain outer peripheraledge. Strictly controlling these factors so as to achieve uniformity,and getting the fluctuation in pullback length between the ceramicsintered member outer peripheral edge and the resistive heating elementsubstantive-domain outer peripheral edge to be essentially within ±0.8%,desirably within ±0.5%, yields the superior isothermal propertiesmentioned above. It should be understood that the pullback length can beappropriately determined according to the wafer or similar target.

As a method for in this way controlling fluctuations in the pullbacklength to be within a certain range, printing, with a paste in whichresistive-heating-element components and a sintering promoter have beenmixed and kneaded, a sintered ceramic body—which after having alreadybeen sintered will not shrink/deform any further—with a circuit, andsubsequently baking the circuit, onto a surface that has been processedto satisfactory precision enables the resistive heating element circuitto be baked without being deformed. By thereafter joining the sinteredceramic body on which the resistive heating element circuit is baked anda sintered ceramic body of identical outside diameter, employing abonding material, a ceramic susceptor inside of which a resistiveheating element is embedded can be readily manufactured. Alternatively,by coating the resistive heating element superficially with a protectivelayer a ceramic susceptor including a resistive heating element can bereadily manufactured.

From the perspectives of corrosion resistance, thermal conductivity, andthe like, it is preferable that the ceramic forming the sintered ceramicbody be made of one substance type selected from aluminum nitride,silicon nitride, silicon carbide, and aluminum oxide.

Likewise, a metal having corrosion resistance and an inherent resistancevalue suited to generating heat, preferably at least one metal typeselected from W, Mo, Ag, Pt, Pd, Ni and Cr, can be used for theresistive heating element.

Embodiments

Embodiment 1—A granulated powder was prepared by adding 0.8 weight %yttrium oxide (Y₂O₃) as a sintering promoter and polyvinyl alcohol as abinder to aluminum nitride (AlN) powder, dispersing and mixing theseingredients using a ball mill with ethanol as a solvent, and thenspray-drying the mixture to granulate it.

After being sintered the granulated powder obtained was molded with auniaxial press into 2 plates whose dimensions were 355 mm diameter×5 mmthickness. These were degreased within a nitrogen gas stream at atemperature of 800° C. and then sintered at 1850° C. in a nitrogen gasstream, whereby sintered AlN plates were manufactured. The thermalconductivity of the sintered AlN plates was 180 W/mK. Both the top andbottom surfaces of the obtained sintered AlN plates were polished usingdiamond grit.

Next, a coil-shaped pattern was printed onto one of the sintered AlNplates using a tungsten slurry that was obtained by kneading and mixingtungsten powder to which 1 weight % yttrium and, as a binder,ethyl-cellulose were added. The final pullback length of the outerperipheral edge of the tungsten-pattern and the outer peripheral edge ofthe sintered AlN plate was set herein to be 1.0 mm. The sintered AlNplate was degreased in a 90° C. nitrogen gas stream, and then baked 2hours as 1800° C.

Further, ethyl-cellulose was added to, mixed with, and kneaded into aY₂O₃—Al₂O₃ bonding material, which mixture was printed as pattern on theone further sintered AlN plate. This was degreased within a 900° C.nitrogen gas stream, and then the tungsten-pattern face andbonding-material face of the two sintered AlN plates were matched andhot-press bonded under 50 g/cm² at 1750° C. The outer periphery of thejoined body was thereafter processed to finish it into a round contour350 mm in diameter.

Power was supplied through externally accessible lead lines from thecircuit ends to the obtained ceramic susceptor, heating the tungstenresistive heating element, and results of measuring the isothermalrating in the wafer-retaining face indicated a satisfactory isothermalrating of 500° C. ±0.40%. In this case, the ceramic susceptor wasbreached along the radial direction and the pullback length between theouter-peripheral edge of the tungsten resistive heating element domain,and the outer peripheral edge of the sintered AlN body, (set value: 1.0mm) was measured, wherein the fluctuation was ±0.2%.

Embodiment 2—A ceramic susceptor that, apart from being printed with apattern in which the outer peripheral edge of the resistive heatingelement domain was distorted by changing only the pattern of thetungsten resistive heating element, was the same as that of Embodiment 1was manufactured. Fluctuation in the pullback length between theresistive heating element domain outer-peripheral edge, and the sinteredAlN body outer peripheral edge was measured in the same manner as withEmbodiment 1, with regard to obtained ceramic susceptors of three kinds;and the isothermal rating of the wafer-retaining face was also measured.

Results were that when the fluctuation in pullback length was ±0.5%, theisothermal rating of the wafer-retaining face was 500° C. ±0.50%.Likewise, when the fluctuation in pullback length was ±0.75%, theisothermal rating was 500° C. ±0.70%. And further, when the fluctuationin pullback length was ±0.8%, the isothermal rating was 500° C. ±0.95%.

Embodiment 3—A granulated powder was prepared by adding 0.8 weight %boron carbide (B₄C) as a sintering promoter and polyvinyl alcohol as abinder to silicon carbide (SiC) powder, dispersing and mixing theseingredients using a ball mill with ethanol as a solvent, and thenspray-drying the mixture to granulate it.

After being sintered the granulated powder obtained was molded with auniaxial press into 2 plates whose dimensions were 355 mm diameter×5 mmthickness. These were degreased within a nitrogen gas stream at atemperature of 900° C. and then sintered 5 hours at 1950° C., wherebysintered SiC plates were manufactured. The thermal conductivity of thesintered SiC plates was 180 W/mK. Both the top and bottom surfaces ofthe obtained sintered SiC plates were polished using diamond grit.

Formation of a tungsten resistive-heating-element circuit and bonding ofthe two sintered plates was carried out by the same techniques as withEmbodiment 1; and the same evaluation as with Embodiment 1 was conductedon the ceramic susceptor obtained, wherein the fluctuation in thepullback length was ±0.3%, while the isothermal rating of thewafer-retaining face was 500° C. ±0.46%.

Embodiment 4—A granulated powder was prepared by adding 2 weight %yttria and 1 weight % alumina as sintering promoters and polyvinylalcohol as a binder to silicon nitride (Si₃N₄) powder, dispersing andmixing these ingredients using a ball mill with ethanol as a solvent,and then spray-drying the mixture to granulate it.

After being sintered the granulated powder obtained was molded with auniaxial press into 2 plates whose dimensions were 355 mm diameters ×5mm thickness. These were degreased within a nitrogen gas stream at atemperature of 900° C. and then sintered 4 hours at 1600° C., wherebysintered Si₃N₄ plates were manufactured. The thermal conductivity of thesintered Si₃N₄ plates was 22 W/mK. Both the top and bottom surfaces ofthe obtained sintered Si₃N₄ plates were polished using diamond grit.

Further, ethyl-cellulose was added to, mixed with, and kneaded into alow-melting-point glass bonding material, which mixture was printed aspattern on the one further sintered Si₃N₄ plate. This was degreasedwithin a 700° C. atmospheric air stream, and then the tungsten-patternface and bonding-material face of the two sintered Si₃N₄ plates werematched and hot-press bonded under 10 g/cm² at 800° C. The outerperiphery of the joined body was thereafter processed to finish it intoa round contour 350 mm in diameter.

The same evaluation as with Embodiment 1 was conducted on the ceramicsusceptor obtained, wherein the fluctuation in the pullback length was±0.3%, while the isothermal rating of the wafer-retaining face was 500°C. ±0.45%.

Embodiment 5—A powder prepared by adding to, and dispersing into andmixing together with, aluminum oxide (Al₂O₃) powder 1 weight % magnesia(MgO) as a sintering promoter and polyvinyl alcohol as a binder, anddrying the mixture, was molded with a uniaxial press into 2 plates whosepost-sintering dimensions were 355 mm diameter×5 mm thickness.

These were degreased within an atmospheric air stream at a temperatureof 700° C. and then sintered 3 hours at 1600° C., whereby sinteredplates were produced. The thermal conductivity of the Al₂O₃ plates was20 W/mK. Both the top and bottom surfaces of the obtained sintered Al₂O₃plates were polished using diamond grit.

Formation of a tungsten resistive-heating-element circuit and bonding ofthe two sintered plates was carried out by the same techniques as withEmbodiment 4; and the same evaluation as with Embodiment 1 was conductedon the ceramic susceptor obtained, wherein the fluctuation in thepullback length was ±0.3%, while the isothermal rating of thewafer-retaining face was 500° C. ±0.46%.

Embodiment 6—By a technique that, apart from a paste for forming theresistive-heating-element circuit being rendered by adding 1 weight %yttria to molybdenum powder and to this mixing in by kneadingethyl-cellulose as a binder, was the same as that of Embodiment 1,ajoined body from sintered AlN plates was fabricated, and in the samemanner thereafter a ceramic susceptor was manufactured.

The same evaluation as with Embodiment 1 was conducted on the ceramicsusceptor obtained, wherein the fluctuation in the pullback lengthbetween the outer-peripheral edge of the molybdenum resistive heatingelement domain, and the outer peripheral edge of the sintered AlN bodywas ±0.3%, while the isothermal rating of the wafer-retaining face was500° C. ±0.46%.

Embodiment 7—Two sintered aluminum nitride plates were produced by thesame method as with Embodiment 1. Utilizing a paste in which a sinteringpromoter and as a binder ethyl-cellulose were added and knead-mixed intoAg—Pd powder, a circuit was formed on one of the plates, which was bakedin air at 900° C. The same method as with Embodiment 4 was utilized fora way of joining these with one further sintered-aluminum-nitride plate.

The same evaluation as with Embodiment 1 was conducted on the ceramicsusceptor obtained, wherein the fluctuation in the pullback lengthbetween the outer-peripheral edge of the Ag—Pd resistive heating elementdomain, and the outer peripheral edge of the sintered AlN body was±0.3%, while the isothermal rating of the wafer-retaining face was 500°C. ±0.45.

Embodiment 8—Two sintered aluminum nitride plates were produced by thesame method as with Embodiment 1. Utilizing a paste in which a sinteringpromoter and as a binder ethyl-cellulose were added and knead-mixed intoNi—Cr powder, a circuit was formed on one of the plates, which was bakedin air at 700° C. The same method as with Embodiment 4 was utilized fora way of joining these with one further sintered-aluminum-nitride plate.

The same evaluation as with Embodiment 1 was conducted on the ceramicsusceptor obtained, wherein the fluctuation in the pullback lengthbetween the outer-peripheral edge of the Ni—Cr resistive heating elementdomain, and the outer peripheral edge of the sintered AlN body was±0.3%, while the isothermal rating of the wafer-retaining face was 500°C. ±0.46.

Embodiment 9—A substrate onto which was baked a tungsten resistiveheating element was produced by the same method as with Embodiment 1.Onto this resistive heating element was spread 100 □m of a paste inwhich Y₂O₃ and ethyl-cellulose binder were knead-mixed into aluminumnitride powder. This was degreased within nitrogen at 900° C. baked 2hours at 1800° C.

The same evaluation as with Embodiment 1 was conducted on the ceramicsusceptor obtained, wherein the fluctuation in the pullback lengthbetween the outer-peripheral edge of the tungsten resistive heatingelement domain, and the outer peripheral edge of the sintered AlN bodywas ±0.2%, while the isothermal rating of the wafer-retaining face was500° C. ±0.40.

COMPARATIVE EXAMPLE 1

Two molded aluminum nitride plates were fabricated by the same method aswith Embodiment 1. One plate was spread with the same tungsten paste asin Embodiment 1, while the one other plate was spread with the samebonding-material paste³ as in Embodiment 1. The two plates were stackedmatching the tungsten-paste face with the bonding-material-paste face,and while 50 kfg/cm² pressure was applied were simultaneously baked at1850° C.

The same evaluation as with Embodiment 1 was conducted on the ceramicsusceptor obtained, wherein isothermal rating in the wafer-retainingface was 500° C. ±1.30%. Further, the ceramic susceptor was breachedalong the radial direction and fluctuation in the pullback lengthbetween the outer-peripheral edge of the tungsten resistive heatingelement domain, and the outer peripheral edge of the sintered AlN bodywas measured, wherein it was ±1.2%.

COMPARATIVE EXAMPLE 2

Two molded aluminum nitride plates were fabricated by the same method aswith Embodiment 1. A groove 4.5 mm in width, 2.5 mm in depth was formedin each. A molybdenum coil was trained into the groove, and the 2 moldedplates were stacked together so as to build—in the molybdenum coil andwere hot-press sintered in nitrogen for 2 hours under 100 kfg/cm², 1850°C.

The same evaluation as with Embodiment 1 was conducted on the ceramicsusceptor obtained, wherein isothermal rating in the wafer-retainingface was 500° C. ±1.70%. Further, the ceramic susceptor was breachedalong the radial direction and fluctuation in the pullback lengthbetween the outer-peripheral edge of the tungsten resistive heatingelement domain, and the outer peripheral edge of the sintered AlN bodywas measured, wherein it was ±1.5.

Only selected embodiments have been chosen to illustrate the presentinvention. To those skilled in the art, however, it will be apparentfrom the foregoing disclosure that various changes and modifications canbe made herein with out departing from the scope of the invention asdefined in the appended claims. Furthermore, the foregoing descriptionof the embodiments according to the present invention is provided forillustration only, and not for limiting the invention as defined by theappended claims and their equivalents.

1. A ceramic susceptor, comprising: a plate-shaped sintered ceramicbody; a resistive heating element formed in or on said ceramic body,said resistive heating element defining a substantive domain having anouter peripheral edge; wherein fluctuation in pullback length betweenthe outer peripheral edge of the sintered ceramic body and the outerperipheral edge of the resistive heating element in its substantivedomain is within ±0.8%.
 2. The ceramic susceptor set forth in claim 1,wherein fluctuation in said pullback length is within ±0.5%.
 3. Theceramic susceptor set forth in claim 1, wherein said sintered ceramicbody is made of at least one substance type selected from aluminumnitride, silicon nitride, silicon carbide, and aluminum oxide.
 4. Theceramic susceptor set forth in claim 2, wherein said sintered ceramicbody is made of at least one substance type selected from aluminumnitride, silicon nitride, silicon carbide, and aluminum oxide.
 5. Theceramic susceptor set forth in claim 1, wherein said resistive heatingelement is made of at least one metal type selected from W, Mo, Ag, Pt,Pd, Ni and Cr.
 6. The ceramic susceptor set forth in claim 2, whereinsaid resistive heating element is made of at least one metal typeselected from W, Mo, Ag, Pt, Pd, Ni and Cr.
 7. The ceramic susceptor setforth in claim 3, wherein said resistive heating element is made of atleast one metal type selected from W, Mo, Ag, Pt, Pd, Ni and Cr.
 8. Theceramic susceptor set forth in claim 4, wherein said resistive heatingelement is made of at least one metal type selected from W, Mo, Ag, Pt,Pd, Ni and Cr.